35 research outputs found
Constraints on the Equation-of-State of neutron stars from nearby neutron star observations
We try to constrain the Equation-of-State (EoS) of supra-nuclear-density
matter in neutron stars (NSs) by observations of nearby NSs. There are seven
thermally emitting NSs known from X-ray and optical observations, the so-called
Magnificent Seven (M7), which are young (up to few Myrs), nearby (within a few
hundred pc), and radio-quiet with blackbody-like X-ray spectra, so that we can
observe their surfaces. As bright X-ray sources, we can determine their
rotational (pulse) period and their period derivative from X-ray timing. From
XMM and/or Chandra X-ray spectra, we can determine their temperature. With
precise astrometric observations using the Hubble Space Telescope, we can
determine their parallax (i.e. distance) and optical flux. From flux, distance,
and temperature, one can derive the emitting area - with assumptions about the
atmosphere and/or temperature distribution on the surface. This was recently
done by us for the two brightest M7 NSs RXJ1856 and RXJ0720. Then, from
identifying absorption lines in X-ray spectra, one can also try to determine
gravitational redshift. Also, from rotational phase-resolved spectroscopy, we
have for the first time determined the compactness (mass/radius) of the M7 NS
RBS1223. If also applied to RXJ1856, radius (from luminosity and temperature)
and compactness (from X-ray data) will yield the mass and radius - for the
first time for an isolated single neutron star. We will present our
observations and recent results.Comment: refereed NPA5 conference proceedings, in pres
Structure and kinetics in the freezing of nearly hard spheres
We consider homogeneous crystallisation rates in confocal microscopy
experiments on colloidal nearly hard spheres at the single particle level.
These we compare with Brownian dynamics simuations by carefully modelling the
softness in the interactions with a Yukawa potential, which takes account of
the electrostatic charges present in the experimental system. Both structure
and dynamics of the colloidal fluid are very well matched between experiment
and simulation, so we have confidence that the system simulated is close to
that in the experiment. In the regimes we can access, we find reasonable
agreement in crystallisation rates between experiment and simulations, noting
that the larger system size in experiments enables the formation of critical
nuclei and hence crystallisation at lower supersaturations than the
simulations. We further examine the structure of the metastable fluid with a
novel structural analysis, the topological cluster classification. We find that
at densities where the hard sphere fluid becomes metastable, the dominant
structure is a cluster of m=10 particles with five-fold symmetry. At a particle
level, we find three regimes for the crystallisation process: metastable fluid
(dominated by m=10 clusters), crystal and a transition region of frequent
hopping between crystal-like environments and other (m\neq10) structuresComment: 10 page
Negative parental responses to coming out and family functioning in a sample of lesbian and gay young adults
Parental responses to youths' coming out (CO) are crucial to the subsequent adjustment of children and family. The present study investigated the negative parental reaction to the disclosure of same-sex attraction and the differences between maternal
and paternal responses, as reported by their homosexual daughters and sons. Participants' perceptions of their parents' reactions (evaluated through the Perceived Parental Reactions Scale, PPRS), age at coming out, gender, parental political
orientation, and religiosity involvement, the family functioning (assessed through the Family Adaptability and Cohesion Evaluation Scales, FACES IV), were assessed in 164 Italian gay and lesbian young adults. Pearson correlation coefficients were calculated to assess the relation between family functioning and parental reaction to CO. The paired sample t-test was used to compare mothers and fathers' scores on the PPRS. Hierarchical multiple regression was conducted to analyze the relevance of each variable. No differences were found between mothers and fathers in their reaction to the disclosure. The analysis showed that a negative reaction to coming out was predicted by parents' right-wing political conservatism, strong religious beliefs, and
higher scores in the scales Rigid and Enmeshed. Findings confirm that a negative parental reaction is the result of poor family resources to face a stressful situation and a strong belief in traditional values. These results have important implications in both clinical and social fields
On measuring colloidal volume fractions
Hard-sphere colloids are popular as models for testing fundamental theories
in condensed matter and statistical physics, from crystal nucleation to the
glass transition. A single parameter, the volume fraction (phi), characterizes
an ideal, monodisperse hard-sphere suspension. In comparing experiments with
theories and simulation, researchers to date have paid little attention to
likely uncertainties in experimentally-quoted phi values. We critically review
the experimental measurement of phi in hard-sphere colloids, and show that
while statistical uncertainties in comparing relative values of phi can be as
low as 0.0001, systematic errors of 3-6% are probably unavoidable. The
consequences of this are illustrated by way of a case study comparing
literature data sets on hard-sphere viscosity and diffusion.Comment: 11 page
Quantitative imaging of concentrated suspensions under flow
We review recent advances in imaging the flow of concentrated suspensions,
focussing on the use of confocal microscopy to obtain time-resolved information
on the single-particle level in these systems. After motivating the need for
quantitative (confocal) imaging in suspension rheology, we briefly describe the
particles, sample environments, microscopy tools and analysis algorithms needed
to perform this kind of experiments. The second part of the review focusses on
microscopic aspects of the flow of concentrated model hard-sphere-like
suspensions, and the relation to non-linear rheological phenomena such as
yielding, shear localization, wall slip and shear-induced ordering. Both
Brownian and non-Brownian systems will be described. We show how quantitative
imaging can improve our understanding of the connection between microscopic
dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of
methodology. Submitted for special volume 'High Solid Dispersions' ed. M.
Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009);
22 pages, 16 fig
Brilliant x-ray radiation from a low emittance 855 MeV electron beam
Electron storage rings as synchrotron radiation sources are presently the most powerful x-ray sources in the energy range between 0.53 keV, the "water window" for microscopy of biological molecules, and 33.16 keV, the K-edge of iodine for a possible coronary angiography. However, with the advent of modern electron accelerators delivering high current low emittance electron beams with energies up to a few GeV it was realized that they may present also attractive sources of intense x rays. In this contribution we report on the investigation of resonant transition radiation in the x-ray region (XTR), and parametric x-ray radiation (PXR) as such x-ray sources. The experiments have been performed with the low emittance (3 it nm rad) 855 MeV electron beam of the Mainz Microtron MAMI....DFG (SFB 201) and BMFT under contract MZ 565.DFG (SFB 201) and BMFT under contract MZ 565.Approved for public release; distribution is unlimited